How many hours must completely discharged rechargeable batteries be recharged by the system?

The correct timeframe for recharging completely discharged rechargeable batteries is 4-8 hours. This duration ensures that the batteries receive a sufficient charge without being overcharged, which can damage their longevity and performance. Charging within this recommended range allows the battery's chemistry to stabilize, which is crucial for maintaining optimal function and efficiency in devices that rely on these batteries.

The other options do not adequately reflect the necessary time frame. Charging for 2-4 hours might not provide enough time for a fully discharged battery to reach a healthy charge level, potentially leading to underperformance. Options of 4-6 hours or 6-8 hours, while close, either underrepresent or exceed the ideal range while not adhering to the standard practices for battery care and longevity. Thus, the 4-8 hour window aligns perfectly with safe charging practices for completely discharged rechargeable batteries.